Effort is underway to develop an enumeration assay for infectious AIDS retrovirus. Such an assay would facilitate more accurate and sensitive titration of virus in tissues and body fluids as well as provide a more sensitive means of detecting virus neutralization by antibodies. The assay we are developing would involve detection of foci of infection in vitro in attached cell monolayers by cytopathic effect or focal indirect immunofluorescence using virus-specific antisera. Thus far, we have mutagenized a nonattached cell line which is permissive for AIDS retrovirus and have derived drug resistant and sensitive clones of this cell line. These clones have been fused to attached cell lines and fused progeny have been selected for attachment to plastic and drug resistance. We are now testing fused clones for susceptibility to infection by AIDS retrovirus. This project is also being expanded to attempt to generate AIDS virus-specific monoclonal antibodies which will detect cell surface virus envelope protein and thus be of potential use in a focal immunofluorescence assay for AIDS virus.